Fig. 4. Optical coherent control of spin.

a Trion level structure in Voigt magnetic field geometry with transitions relevant for the spin-initialization, rotation, and read-out. Inset: For the spin rotation a stimulated Raman transition using circularly polarized pulses is used which in case of small detuning can be effectively reduced to spin-rotation of a two-level system. b Pulse sequence used to coherently rotate the spin. The first pulse injects the charge into the QD and a cw spin-pumping laser initializes the spin into the $∣\Uparrow ⟩$ state. After 6 ns a circularly polarized Raman spin-rotation pulse is applied detuned by ~400 GHz from the trion transition. Immediately after spin-rotation into the $∣\Downarrow ⟩$ state, the cw laser excites the system into $∣\downarrow \Uparrow \Downarrow ⟩$ and a photon is emitted. c Emission time trace of the $∣\downarrow \Uparrow \Downarrow ⟩$-$∣\Uparrow ⟩$ transition in the presence and absence of the cw spin-pumping/read-out laser. d Emission intensity after the spin-rotation pulse as a function of the square root of the rotation pulse power. Clear Rabi oscillations are visible up to 3π demonstrating coherent control. Inset: Bloch sphere representation of the hole qubit evolution with the rotation pulse power.